When computer equipment is brought into standby mode (known in the art as the “S3” mode), the working memory (RAM) of the computer is kept powered so as to preserve the data therein ready for a next power-up of the computer The RAM is conventionally powered in the S3 condition by a specific power source, or “standby rail”. Computer equipment is generally provided with input/output (I/O) ports including a power supply conductor for powering peripheral devices connected to such ports. The same standby rail which powers the RAM is also conventionally used for providing power to these I/O ports. This is also typically the case for Universal Serial Bus (USB) ports, which need to have power active during the standby mode of the computer.
In such a situation, that is, when a USB peripheral device is connected to a USB port, the peripheral can draw significant current from the power conductor of said port On the other side, the standby rail of a conventional computer is typically capable of delivering a current of 1 or 2 Amps. this value being primarily governed by the current which is drawn by the RAM chips during S3 mode.
Therefore, should a USB peripheral draw a high current from the USB port, this can cause the standby rail voltage to drop, to the extent that the RAM chips will be no longer properly powered and data stored therein will be lost.
It has been proposed to provide dedicated power supply chips for handling such situations in relation to USB ports or in other environments. Such solutions are however expensive as they are based on a per-port approach. Thus that if the number of I/O ports is increased, and given that there is nowadays a tendency to provide personal computers with 6 or 8 USB ports or even more, the number of dedicated supply chips also has to be increased. This is costly and additionally requires appropriate room on the USB board or mother board.
A further drawback of these known supply chips is that they individually act as current limiters, without taking into account the fact that a plurality of USB ports may altogether draw a cumulative current that will still cause the voltage source to drop and cause loss of RAM contents.
Therefore, this known technique is expensive and cumbersome while falling to safely prevent data losses, in particular when numerous USB ports are provided.